The process of manufacturing liquid containers from polymeric materials has been widely used for many decades now. More specifically, such containers are often manufactured using a stretch blow molding process in which a pre-manufactured preform is softened by heating and then inserted into a blow mold. By first mechanically stretching the softened preform using a stretch rod and second blowing high pressure air into the preform, the preform is expanded until its shape conforms to the inner surface of the blow mold and thus forms—after cooling—a shaped container, such as a bottle. At the end, the shaped container is removed from the mold and transferred over to downstream processing steps such as filling, closing, and labeling.
Producing a filled container using the known stretch blow molding process, however, always requires two separate steps, blowing and filling. Due to the different natures of these two steps and the time it takes to complete them, these two process steps are typically carried out by two different machines which are operating sequentially in the same manufacturing line. In some instances, empty containers are even produced in one factory and shipped to a second factory in order to be filled at a later point in time. Many state of the art filling machines rely on gravitational flow of the liquid consumable into the empty container. Often, the fill nozzle does not touch the neck of the container during the filling process such that using an elevated pressure for urging the liquid into the container without causing significant spillage is not possible. Such a filling process relying on gravitational forces takes considerable time—especially for large bottles—of ten to twenty seconds per bottle and more.
It has already been suggested (see for example U.S. Pat. No. 3,267,185 published on Aug. 16, 1966) to combine the steps of expanding the preform into a shaped container and of filling the shaped container by using the consumable liquid as the fluid medium for imparting the pressure onto the preform to cause its expansion. After this step, the consumable liquid is already inside the container and the subsequent filling step is no longer necessary. This process of simultaneously forming and filling a shaped container is termed hydraulic forming. In a system described in U.S. Pat. No. 3,267,185 mold stations circulate along a circular path. A tube is extruded along the circular path. The tubular parison is progressively closed, forming a first end of the future container. Then the closed tubular shape is filled and expended. Then the other end of the future container is closed and cut. A drawback of such a system is that the throughput is very low.
Industrializing the process of manufacturing filled shaped containers from polymeric materials usually takes the form of rotary machines, each comprising a rotary wheel. A plurality of rotary machines is coupled to form a manufacturing line. The manufactured container is transported along an arcuate path by the rotation of the rotary wheel of the first machine and then transferred to the second machine where it is again transported by rotation of the rotary wheel along an arcuate path. That way, a continuous manufacturing process which can accommodate high manufacturing throughputs is made possible. Linear machines—in contrast thereto—operate in batch mode only and cannot be accelerated to achieve the same high throughputs at which rotary machines can be operated. Linear machines are used only under exceptional circumstances such as low output equipment.
An apparatus described in US2012/0048683A1 comprises a transport device having a central rotation axis. A receiver device, for example a gripper clamp, receives a preform. The receiver device has a swivel movement driven by a servo drive such that the resulting force extends in the longitudinal direction of the preform. US2012/0048683A1 further describes an air blow machine having a blow mold, a stretch rod for forming a preform. All the described embodiments have the neck of the preform oriented outwardly with respect to the machine rotation axis. Upon rotation of the machine, a compression force is exerted on the lower section of the preform including the closed end of the preform.
Document W02013/020885 describes in its FIG. 3 a rotary system for simultaneously blowing and filling plastic containers. The longitudinal axes of the molding stations are inclined at 45° relative to the vertical axis. The document explains that this inclination makes it possible to avoid splashing of the liquid due to the centrifugal force exerted on the liquid in motion.
The inventors of the current invention have discovered that the example of an inclination of 45° indicated in W02013/020885 is an optimized value of the inclination for preventing spillage for almost any rotational speed. As illustrated in FIG. 1a, when the container 21 has been expanded up to the shape of the mold 22 and is full of liquid 23, the injection nozzle 24 is retracted and an head space 25 free of liquid is provided, for example during the nozzle retraction. Therefore, there is a free level of liquid 26 inside the formed container with the atmospheric pressure above it. The orientation of the free level of liquid depends on the rotation speed of the machine. If the rotation speed is very low or null, the free level of liquid would be almost horizontal as illustrated in FIG. 1a. The liquid free level is inclined by almost 45° inside the container. The size of the free head space 25 is such that the liquid is still contained in the container without splashing. FIG. 1b illustrates the position of the free level when the centrifugal acceleration 27 due to the rotation speed is more than 4 times the gravity acceleration 28. The liquid free space is almost vertical and so inclined by 45° inside the container. There is no splashing.
The inventors of the current invention have further discovered a drawback of the rotary system described in W02013/020885, which is illustrated in the current FIG. 1c. The forming method may include introducing the stretch rod 29 down to the bottom of the heated preform 30. The stretching force exerted by the stretch rod contributes to keep the bottom 31 of the preform 30 well centered inside the cavity 32. When the liquid is injected in the preform, the centrifugal acceleration 27 exerted on the liquid tends to move the liquid and the central part of the preform 30 outwardly, and to bend the preform 30 even if the preform is guided by its neck 33 and by its bottom 31. This may provoke cold spots 34 on the container when the central part of the preform 30 under expansion comes too early in contact with the cold wall of the mold 22 or of the stretch rod 29. This may provoke some container blowouts. That phenomenon did not exist when the forming fluid was air, wherein the tension of the preform 30 provided by the stretch rod is high enough to keep the preform well centered inside the cavity all along the expansion phase. With a forming fluid being a liquid, guiding the preform by it neck and by its bottom may not be sufficient to avoid cold spots and blowouts.
A further complexity for rotary apparatus and processes is that the shaped container should preferably be removed from the mold after hydraulic forming in an upright position in order to reduce the risk of spillage and provide for transferability to further processing on rotary machines. If the shaped container is removed from the mold in a tilted orientation in order to accommodate for centrifugal forces while being expanded on the forming wheel, this tilt would have to be reversed or at least be eliminated before the shaped container can be placed on the arcuate manufacturing path of a downstream rotary wheel which must rotate in the opposite direction.
It is accordingly desirable to overcome the above disadvantages of the prior art machines for manufacturing filled shaped containers. In one aspect, it is desirable to develop a rotary machine which is capable of performing the hydraulic forming process at high throughputs. It is another aspect to develop a rotary process for hydraulic forming of shaped containers. It is another aspect to provide a rotary apparatus and a rotary process for hydraulic forming of shaped containers which reduce the detrimental effect of centrifugal forces acting on the expanding preform.